The study involved four groups of adult participants in 11 countries and followed them up for over a year. The groups constituted 311 non-smokers with severe asthma, 110 smokers and ex-smokers with severe asthma, 88 patients with milder asthma and 101 healthy volunteers.

The results found that patients with severe asthma had more symptoms and exacerbations compared to patients with mild-moderate disease. Severe asthma patients also reported worse quality of life and higher levels of anxiety and depression as well as more nasal polyps (small growths in the nose), acid indigestion and poorer lung function.

A key finding is that although patients with severe asthma take greater amounts of anti-inflammatory treatment, including inhaled and oral steroids, they still had higher levels of inflammation in their airways.

This study is the first to describe severe asthma across such a large cohort."Once we can break this condition down into different groups, patients can be swiftly and accurately diagnosed and individually treated by targeting the mechanisms that are driving their own disease," explained lead author Dominick Shaw from University of Nottingham.

"Once we can identify these new treatments, we can lessen the burden of this chronic and debilitating disease," he added. The new paper, published in the European Respiratory Journal, is one of the largest assessments of adults with severe asthma to date, looking at several characteristics including symptoms, patients' quality of life and blood and airway measurements.